That might not have been the case had such big strides in diesel technology not been made over the past few decades.

It's gone from a fuel with dubious environmental credentials to one that challenges gasoline and natural gas for cleanliness, all the while offering better fuel economy and does so at an effective price point.

The advent of low-sulfur fuels in 2006-2007 allowed diesel to significantly clean up its act. It allowed engine-builders to develop ways of cutting diesel exhaust emissions that otherwise wouldn't have been possible, as sulfur can attack the elements used in after-treatment technologies.

As particulate traps and urea injection have cleaned up diesel fumes in passenger cars, so too have similar technologies improved heavy-duty engines in trucks.

The improvement is clear to see: A truck manufactured after 2007 emits just two percent of the pollutants a truck made in 1988 did.

They're more fuel-efficient too, by three to five percent. Schaeffer quotes figures suggesting class 4-8 trucks on the road today save 13.3 million barrels of crude oil per year compared to their counterparts from a few decades ago--and produce 5.7 million fewer tonnes of CO2.

Pricing is steadier than that of natural gas, which fluctuates through global demand and as techniques like fracking vary supply of the gas.

Diesel is more expensive right now, but Schaeffer suggests operators are as concerned about predictability as much as they are cost--stability is key when planning for the future. He also says that current long-term gas deals cloud the real cost of natural gas fuels--a cost that could one day hit operators.

The end result is that by 2040, diesel could account for 70 percent of all transportation fuels, while natural gas rises from today's one percent to a still-modest 4 percent of the market.

While not mentioned in the article, it's also worth noting that diesel is still the more widely-available fuel right now--and that situation is unlikely to change for natural gas unless operators demand it. And they're unlikely to demand natural gas trucks without stations to fuel them...

While someone writing from the Diesel Technology Forum on an outlet funded by General Electric might be taken with a pinch of salt when discussing diesel, it's hard not to see diesel being the dominant truck fuel for some time to come.

But as with passenger vehicles, we're likely to see a real mix over the coming years--diesel may be dominant, but it won't be the only fuel, and for a select few, natural gas will remain the less expensive, potentially cleaner way of moving goods from place to place.